1. Field of the Invention
The present invention relates to a reactor containing a packed bed of a catalyst, an absorbent or the like, and particularly to a reactor called a radial flow reactor configured such that a reactor vessel thereof is tubular and a fluid passes through the packed bed in a radial direction thereof.
2. Background of the Invention
In a typical radial flow reactor, the reactor is cylindrical and is disposed upright. Inside a reactor vessel, a center pipe, a packed bed, and an outer basket are arranged in this order from the center outward in a cross section perpendicular to the axial direction of the reactor, namely, in a horizontal cross section. The center pipe is located in the center in the horizontal cross section to form a fluid passage (an inner passage) extending in the axial direction. Fluid can move inside the inner passage in the axial direction and can pass through the wall of the center pipe in the radial direction. The packed bed, which is a continuous bed of granular packing, is disposed around the center pipe and has an annular cross section in the horizontal cross section. A fluid passage (an outer passage) located around the packed bed is formed between the outer basket and an inner surface of the reactor vessel. Fluid can move inside the outer passage in the axial direction and can pass through the wall of the outer basket in the radial direction. The fluid supplied to the reactor vessel flows inside the center pipe in the axial direction, then flows inside the packed bed in the radial direction, and then flows outside the outer basket in the axial direction, or flows outside the outer basket in the axial direction, then flows inside the packed bed in the radial direction, and then flows inside the center pipe in the axial direction. Subsequently, the fluid is discharged from the reactor vessel. When the fluid flows inside the packed bed in the radial direction, a catalytic reaction or an adsorption reaction may occur.
Compared with an axial flow reactor in which the fluid inside the packed bed flows in the axial direction, in the case of the radial flow reactor, it is easy to increase the passage area (cross-sectional area of the passage) of the fluid and reduce the passage thickness (length of the passage) of the packed bed. Therefore, it is easy to reduce the pressure drop between the inlet and the outlet of the reactor. For such an advantage, the radial flow reactor is suitably used when reacting a large amount of fluid while preventing the increase of the pressure drop in the reactor.
In recent years, reactors have been required to be larger in size due to economic or social demands. In this case, due to economic or technical reasons, the common practice is to increase the length of the reactor rather than the diameter of the reactor for a larger size. If the diameter is relatively small, it is possible to construct a pressure vessel using a relatively thinner plate.
However, in the case of the radial flow reactor, when the length of the reactor is increased rather than the diameter of the reactor for a larger size, the fluid passage area may be excessively increased, and hence the flow rate of the fluid in the packed bed may become very low and the pressure loss in the packed bed may become excessively small. Thus, it may be difficult to obtain a uniformly distributed flow with respect to the passage area in the packed bed. In that case, an outer basket or a center pipe having complicated structure is often used in order to intentionally generate resistance to the flow (pressure loss) and to forcibly obtain a uniformly distributed flow with respect to the passage area.
Further, in the case of a radial flow reactor in which heat transfer tubes for heating or cooling are inserted into a packed bed, when the length of the reactor is increased rather than the diameter of the reactor for a larger size, the fluid flow speed in the packed bed may be reduced and a sufficient heat transfer performance may not be achieved.
Such problems can be solved by allowing a fluid to flow through multiple passes in the radial flow reactor.
U.S. Pat. No. 3,372,988 discloses a radial flow reactor with a multi-pass structure in which a gas passes through a catalyst bed a plurality of times. The reactor includes a partition plate which divides the catalyst bed into two or three in the axial direction so that gas passes through the catalyst bed in the radial direction two or three times while the flow direction of the gas is reversed.
JP H03-131336A discloses a radial flow reactor having a packed bed not divided into a plurality of beds, namely, a continuous packed bed. The reactor includes a blocking section disposed in a center pipe to prevent gas from passing in the axial direction and in the radial direction. The reactor also includes a blocking section disposed in an outer basket to prevent gas from passing in the axial direction and in the radial direction. The position of the blocking section arranged in the center pipe is different from the position of the blocking section arranged in the outer basket in the axial direction. These blocking sections change the gas flow direction to allow the gas to pass through the packed bed a plurality of times.